Prediction of plasma ctDNA fraction and prognostic implications of liquid biopsy in advanced prostate cancer

No consensus strategies exist for prognosticating metastatic castration-resistant prostate cancer (mCRPC). Circulating tumor DNA fraction (ctDNA%) is increasingly reported by commercial and laboratory tests but its utility for risk stratification is unclear. Here, we intersect ctDNA%, treatment outcomes, and clinical characteristics across 738 plasma samples from 491 male mCRPC patients from two randomized multicentre phase II trials and a prospective province-wide blood biobanking program. ctDNA% correlates with serum and radiographic metrics of disease burden and is highest in patients with liver metastases. ctDNA% strongly predicts overall survival, progression-free survival, and treatment response independent of therapeutic context and outperformed established prognostic clinical factors. Recognizing that ctDNA-based biomarker genotyping is limited by low ctDNA% in some patients, we leverage the relationship between clinical prognostic factors and ctDNA% to develop a clinically-interpretable machine-learning tool that predicts whether a patient has sufficient ctDNA% for informative ctDNA genotyping (available online: https://www.ctDNA.org ). Our results affirm ctDNA% as an actionable tool for patient risk stratification and provide a practical framework for optimized biomarker testing.

Results of the first international quality control programme for oral targeted oncolytics

AIMS

With the rising number of oral targeted oncolytics and growing awareness of the benefits of therapeutic drug monitoring (TDM) within the field of oncology, it is expected that the requests for quantifying concentrations of these drugs will increase. It is important to (cross-)validate available assays and ensure its quality, as results may lead to altered dosing recommendations. Therefore, we aimed to evaluate the performance of laboratories measuring concentrations of targeted oral oncolytics in a one-time international quality control (QC) programme.

METHODS

Participating laboratories received a set of plasma samples containing low, medium and high concentrations of imatinib, sunitinib, desethylsunitinib, pazopanib, cabozantinib, olaparib, enzalutamide, desmethylenzalutamide and abiraterone, with the request to report their results back within five weeks after shipment. Accuracy was defined acceptable if measurements where within 85%-115% from the weighed-in reference concentrations. Besides descriptive statistics, an exploratory ANOVA was performed.

RESULTS

Seventeen laboratories from six countries reported 243 results. Overall, 80.7% of all measurements were within the predefined range of acceptable accuracy. Laboratories performed best in quantifying imatinib and poorest in quantifying desethylsunitinib (median absolute inaccuracy respectively 4.0% (interquartile range (IQR) 1.8%-6.5%) and 15.5% (IQR 8.8%-34.9%)). The poorest performance of desethylsunitinib might be caused by using the stable-isotope-labelled sunitinib instead of desethylsunitinib as an internal standard, or due to the light-induced cis(Z)/trans(E) isomerization of (desethyl)sunitinib. Overall, drug substance and performing laboratory seemed to influence the absolute inaccuracy (F = 16.4; p < 0.001 and F = 35.5; p < 0.001, respectively).

CONCLUSION

Considering this is the first evaluation of an international QC programme for oral targeted oncolytics, an impressive high percentage of measurements were within the predefined range of accuracy. Cross-validation of assays that are used for dose optimization of oncolytics will secure the performance and will protect patients from incorrect advices.

Effect of Aprepitant on Etoposide Pharmacokinetics in Patients with Testicular Cancer: A Pharmacokinetic Study to Determine the Absence of a Clinically Relevant Interaction

All patients treated with anticancer agents should receive the most effective anti-emetic regimen. Anti-emetic guidelines provide recommendations but do not take into account possible drug-drug interactions between anti-emetics and anticancer drugs. This study determines the clinical relevance of the potential drug-drug interaction of the neurokinin-1 receptor antagonist, aprepitant, on the pharmacokinetics of etoposide. Aprepitant is a moderate CYP3A4 inhibitor and may increase the systemic exposure of etoposide which is partly metabolized by cytochrome P450 enzyme 3A4 (CYP3A4). In this prospective observational study, the pharmacokinetics of etoposide with and without concomitant use of aprepitant was determined in 12 patients receiving first-line chemotherapy for testicular cancer. The geometric mean (95% confidence interval (CI)) area under the plasma concentration-time curve 0-24 hour (AUC0-24h ) of etoposide with aprepitant was 86.2 (79.7-93.2) mg/L*hour vs. 83.7 (75.8-92.4) mg/L*hour without aprepitant. Geometric mean ratios (90% CIs) of AUC0-24h and maximum plasma concentration (Cmax ) for etoposide with and without aprepitant were 1.03 (0.96-1.10) and 0.96 (0.89-1.03), respectively. This study confirms the absence of a clinically relevant interaction between etoposide and aprepitant. Both drugs can be safely combined without affecting etoposide exposure.

PARPing up the right tree; an overview of PARP inhibitors for metastatic castration-resistant prostate cancer

PARP inhibitors (PARPi) are transforming the current treatment landscape of metastatic castration-resistant prostate cancer. By reanalysing published data on olaparib, talazoparib, rucaparib and niraparib, we provide a concise overview of responses by molecular subgroup. As monotherapy, all PARPi showed comparable efficacy and the same hierarchy in responsiveness: patients with tumours harbouring aberrations in BRCA1 or BRCA2 (BRCAm) evidently demonstrate superior responses when compared to aberrations in other homologous recombination repair (HRR) related genes. Niraparib seems to cause more grade ≥3 adverse events in comparison to other PARPi. PARPi have also been combined with androgen-receptor signalling inhibitors (ARSI) for both patients with tumours harbouring aberrations in HRR genes (HRRm), and molecularly unselected patients. Compared to wildtype, BRCAm patients responded best, followed by HRRm. Olaparib-abiraterone, niraparib-abiraterone, and talazoparib-enzalutamide all prolonged progression-free survival compared to an ARSI alone in HRRm patients. In the non-HRRm subgroup, only olaparib-abiraterone and talazoparib-enzalutamide were effective. Results for the combination of rucaparib with enzalutamide are yet to be reported. The rate of grade ≥3 adverse events for the combination regimens is 10-30% higher when compared to an ARSI alone. Given the limited efficacy in unselected patients, these PARPi-ARSI combinations may be best reserved for selected patients.

Pharmacokinetic boosting of olaparib: A randomised, cross-over study (PROACTIVE-study)

BACKGROUND

Pharmacokinetic (PK) boosting is the intentional use of a drug-drug interaction to enhance systemic drug exposure. PK boosting of olaparib, a CYP3A-substrate, has the potential to reduce PK variability and financial burden. The aim of this study was to investigate equivalence of a boosted, reduced dose of olaparib compared to the non-boosted standard dose.

METHODS

This cross-over, multicentre trial compared olaparib 300 mg twice daily (BID) with olaparib 100 mg BID boosted with the strong CYP3A-inhibitor cobicistat 150 mg BID. Patients were randomised to the standard therapy followed by the boosted therapy, or vice versa. After seven days of each therapy, dense PK sampling was performed for noncompartmental PK analysis. Equivalence was defined as a 90% Confidence Interval (CI) of the geometric mean ratio (GMR) of the boosted versus standard therapy area under the plasma concentration-time curve (AUC0-12 h) within no-effect boundaries. These boundaries were set at 0.57-1.25, based on previous pharmacokinetic studies with olaparib capsules and tablets.

RESULTS

Of 15 included patients, 12 were eligible for PK analysis. The GMR of the AUC0-12 h was 1.45 (90% CI 1.27-1.65). No grade ≥3 adverse events were reported during the study.

CONCLUSIONS

Boosting a 100 mg BID olaparib dose with cobicistat increases olaparib exposure 1.45-fold, compared to the standard dose of 300 mg BID. Equivalence of the boosted olaparib was thus not established. Boosting remains a promising strategy to reduce the olaparib dose as cobicistat increases olaparib exposure Adequate tolerability of the boosted therapy with higher exposure should be established.

Therapeutic drug monitoring to personalize dosing of imatinib, sunitinib, and pazopanib: A mixed methods study on barriers and facilitators

BACKGROUND

Personalized dosing based on measurement of individual drug levels and adjusting the dose accordingly can improve efficacy and decrease unnecessary toxicity of oncological treatment. For imatinib, sunitinib, and pazopanib, this therapeutic drug monitoring (TDM)-guided dosing is, however, not routinely used, despite accumulating evidence favoring individualized dosing. Therefore, we aimed to identify and quantify (potential) barriers and facilitators in TDM-guided dosing for imatinib, sunitinib, and pazopanib.

METHODS

We performed a mixed methods study among all stakeholders involved: patients, healthcare professionals (HCPs), pharmaceutical companies, and health insurance companies. During the first qualitative part of this study, we performed semi-structured individual interviews and one focus group interview to identify all (potential) barriers and facilitators, and during the second quantitative part of this study, we used a web-based survey to quantify these findings. The interviews addressed the six domains of the implementation of change model of Grol and Wensing: (1) the innovation itself; (2) the HCP; (3) the patient; (4) social context; (5) organizational context; and (6) finances, law, and governance.

RESULTS

In the qualitative study, we interviewed 20 patients, 18 HCPs and 10 representatives of pharmaceutical and health insurance companies and identified 72 barriers and 90 facilitators. In the quantitative study, the survey was responded by 66 HCPs and 58 patients. Important barriers were on the domain of the HCP, such as a lack of experience with TDM (36.4%), on the domain of the patient, such as lack of awareness of TDM (39.7%), and the processing time for measurement and interpretation of the TDM result (40.9%) (organizational domain). Important facilitators were education of HCPs (95.5%), education of patients (87.9%) and facilitating an overview of when and where TDM measurements are being performed (86.4%).

CONCLUSION

We identified and quantified important barriers and facilitators for the implementation of TDM-guided dosing for imatinib, sunitinib, and pazopanib. Based on our results, the implementation strategy should mainly focus on educating both HCPs and patients and on the organizational aspect of TDM.

Clinical Pharmacokinetics and Pharmacodynamics of the Next Generation Androgen Receptor Inhibitor-Darolutamide

Darolutamide is a next-generation androgen receptor signaling inhibitor (ARSI) currently approved for the treatment of nonmetastatic castration-resistant prostate cancer (nmCRPC) and metastatic hormone sensitive prostate cancer (mHSPC). Studies suggest that darolutamide also has the potential to be used to treat other stages of prostate cancer (PC), suggesting that its indications will broaden in the near future. Since ARSIs show similar efficacy for the treatment of PC, pharmacokinetic properties of these drugs and patient characteristics could help physicians decide which drug to select. This review provides an overview of the pharmacokinetic and pharmacodynamic properties of darolutamide. One of the most important pharmacological advantages of darolutamide is its low brain distribution and therefore limited seizure potential and central nervous system adverse effects. In addition, darolutamide has little drug-drug interaction potential and is unlikely to alter the exposure of other cytochrome P450 or P-glycoprotein substrates. Nevertheless, it may significantly increase the exposure of breast cancer resistant protein (BCRP) substrates. The limited solubility and bioavailability of darolutamide increases when taken together with food, regardless of the fat content. Darolutamide is excessively metabolized by oxidation and glucuronidation and excreted in the urine and feces. For this reason, dose reduction is required in patients with moderate and severe renal or severe hepatic impairment. Although no exposure-response relationship was observed with darolutamide, less advanced stages of PC showed better PSA response on treatment. Overall, darolutamide has some advantageous pharmacological properties that may lead to its preferred use, when broader registered, in selected patients across different disease stages.

Measuring Tumour Imatinib Concentrations in Gastrointestinal Stromal Tumours: Relevant or Redundant?

Imatinib plasma trough concentrations are associated with efficacy for patients treated for advanced or metastatic KIT-positive gastrointestinal stromal tumours (GISTs). This relationship has not been studied for patients treated in the neoadjuvant setting, let alone its correlation with tumour drug concentrations. In this exploratory study we aimed to determine the correlation between plasma and tumour imatinib concentrations in the neoadjuvant setting, investigate tumour imatinib distribution patterns within GISTs, and analyse its correlation with pathological response. Imatinib concentrations were measured in both plasma and in three regions of the resected primary tumour: the core, middle part, and periphery. Twenty-four tumour samples derived from the primary tumours of eight patients were included in the analyses. Imatinib tumour concentrations were higher compared to plasma concentrations. No correlation was observed between plasma and tumour concentrations. Interpatient variability in tumour concentrations was high compared to interindividual variability in plasma concentrations. Although imatinib accumulates in tumour tissue, no distribution pattern of imatinib in tumour tissue could be identified. There was no correlation between imatinib concentrations in tumour tissue and pathological treatment response.

Abstract 4028: High-dose short-exposure of osimertinib robustly inhibits growth of patient-derived metastatic colorectal cancer organoids

Despite major interest in tyrosine kinase inhibitors (TKIs) as a treatment option for metastatic colorectal cancer (mCRC), almost all TKIs tested for mCRC fail in early-phase clinical trials. Although showing specific target inhibition at low concentrations, TKIs have a much broader kinase inhibitory potency at higher concentrations. Alternative high dose regimens have been proposed to explore if efficacy can be improved with acceptable toxicity. We used 3D matrix-embedded tumor organoids as a preclinical platform to determine optimal drug exposure, i.e. preclinical pharmacology, and to dissect the mechanisms of action to potentially convert the dismal translational success rate of TKIs for mCRC. We established patient-derived tumor organoids (PDTOs) from mCRC biopsies and, based on favorable physicochemical and pharmacokinetic properties, selected 3 TKIs (sunitinib, cediranib and osimertinib). Following standard IC50 assessment using continuous dosing with a concentration range, we investigated the cytotoxic antitumor effect of high-dose, short-exposure (HDSE) treatment. Five PDTOs were exposed to 20 µM TKI for 1-24h, washed and given normal medium, and PDTO-outgrowth was determined 1 week later. At exposures of 1, 3 and 6h, we measured intra-tumoroid TKI concentrations using a clinically validated LC/MS-MS method. PDTO cell death was observed using live-cell microscopy, and quantified by both caspase 3/7 enzyme activity assay and cleaved caspase-3 immunofluorescent staining. While PDTOs could be categorized for their sensitivity across tested TKIs, all were highly sensitive for osimertinib (IC50 values 0.40-3.8 µM). Lower sensitivity was observed for sunitinib (2.0-10.5 µM) and cediranib (2.5-7.1 µM). Only for osimertinib exposure to 20 µM for 3h was sufficient to block proliferation in all PDTOs. Interestingly, peak intra-tumoroid TKI concentration measurements across PDTOs revealed marked cellular accumulation, indicating an expanded potential for target inhibition. The concentrations correlated with sensitivity: for sunitinib from 1.5 mM for the most sensitive PDTO to 0.72 mM for the least sensitive PDTO. Likewise, the corresponding cediranib concentrations were 0.15 mM vs 0.062 mM. All PDTOs had high intra-tumoroid osimertinib concentrations (0.90-1.6 mM). Lastly, we detected a significant increase in apoptosis after 3h of HDSE with osimertinib. Whereas our HDSE regimen shows promising results for all 3 TKIs, very short exposure with high-dose osimertinib effectively reduces proliferation and induces cell death in all mCRC PDTOs. While this is likely due to high intra-tumoroid concentrations reached by osimertinib—the mechanism of action at these concentrations remains unknown and is subject to further studies. In parallel, we propose that a HDSE osimertinib regimen warrants clinical exploration as a potential new treatment option for mCRC.

Citation Format: Kirti K. Iyer, Dennis Poel, Anne Miggelenbrink, Wouter Kerkhof, Erik van den Hombergh, Loek A. de Jong, Nielka P. van Erp, Daniele V. Tauriello, Henk M. Verheul. High-dose short-exposure of osimertinib robustly inhibits growth of patient-derived metastatic colorectal cancer organoids. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4028.

Abstract 418: Elacridar potentiates sunitinib efficacy in colorectal cancer models

For unresectable metastatic colorectal cancer (mCRC), the main treatment strategy is combination chemotherapy, targeted therapy, or immunotherapy. Long-term treatment benefit of these therapies is limited to a small subgroup of patients. To improve treatment outcome, many tyrosine kinase inhibitors (TKIs) have been clinically tested in patients with mCRC. Most failed already in early-phase clinical trials due to intrinsic resistance. ATP Binding Cassette Transporter (ABC)B1- and ABCG2-transporters are known contributors to treatment resistance in mCRC. Therefore, we evaluated whether inhibition of these transporters could potentiate the efficacy of TKIs in colorectal cancer (CRC) models.

CRC cell lines, HT29, COLO320 and CACO2 and newly established patient-derived tumor organoids (PDTOs) from mCRC biopsies were first analyzed for the presence of ABCB1 and ABCG2 expression. Models that expressed ABCB1 or ABCG2 were pre-incubated with a non-toxic dose of elacridar, a potent transporter inhibitor, and exposed to a concertation range of three TKIs; sunitinib, cediranib and osimertinib. Next, we measured intracellular drug concentrations using LC/MS-MS one hour after TKI exposure (20 µM) with or without pre-incubation of elacridar. Using the fluorescent properties of sunitinib, we performed live-cell imaging to compare intracellular sunitinib distribution in cells that were or were not pre-incubated with elacridar.

ABCB1 and ABCG2 expression was observed in all CRC models except for HT29 cells, which did not express ABCB1. Pre-incubation with elacridar significantly improved sunitinib efficacy in CRC cells. The IC50 decreased from 2.15 µM to 1.17 µM (p = 0.04), from 1.32 µM to 0.44 µM (p = 0.03), and from 4.94 µM to 3.43 µM (p = 0.03) for HT29, COLO320 and CACO2 cells respectively. This effect was not observed for cediranib and osimertinib. Although not significant, for both PDTO models tested, the IC50 for sunitinib decreased from 8.04 µM to 3.29 µM and from 6.93 µM to 4.16 µM. Intracellular sunitinib concentrations in the tested CRC cell models after sunitinib exposure ranged from 2.46 mM to 4.13 mM without elacridar and from 0.38 mM µM to 1.31 mM when pre-incubated with elacridar (p &lt; 0.01). Live-cell imaging of CRC cells revealed a different pattern of intracellular sunitinib accumulation with and without pre-incubation with elacridar.

Inhibition of multi-drug resistance proteins ABCB1 and ABCG2 with the clinically tested selective transporter inhibitor elacridar potentiates sunitinib efficacy in CRC models. Interestingly, this was accompanied with reduced intracellular sunitinib accumulation. Further research in mCRC PDTOs is warranted to confirm whether this mechanism is involved in intrinsic TKI resistance and therefore contribute to the early-phase failure of clinical trials testing TKIs for mCRC.

Citation Format: Dennis Poel, Kirti K. Iyer, Bob van Gasteren, Beau Dagniaux, Erik van den Hombergh, Nielka P. van Erp, Daniele V. Tauriello, Henk M. Verheul. Elacridar potentiates sunitinib efficacy in colorectal cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 418.

Early on-treatment changes in circulating tumor DNA fraction and response to enzalutamide or abiraterone in metastatic castration-resistant prostate cancer

PURPOSE

Androgen receptor pathway inhibitors (ARPI) are standard of care for treatment-naive metastatic castration-resistant prostate cancer (mCRPC), but rapid resistance is common. Early identification of resistance will improve management strategies. We investigated whether changes in circulating tumor DNA (ctDNA) fraction during ARPI treatment are linked with mCRPC clinical outcomes.

EXPERIMENTAL DESIGN

Plasma cell-free DNA was collected from 81 patients with mCRPC at baseline and after 4-weeks of first-line ARPI treatment during two prospective multi-centre observational studies (NCT02426333;NCT02471469). CtDNA fraction was calculated from somatic mutations in targeted sequencing and genome copy number profiles. Samples were classified into detected vs. undetected ctDNA. Outcome measurements were progression-free survival (PFS) and overall survival (OS). Non-durable treatment response was defined as PFS ≤ 6 months.

RESULTS

CtDNA was detected in 48/81 (59%) baseline and 29/81 (36%) 4-week samples. CtDNA fraction for samples with detected ctDNA was lower at 4-weeks vs. baseline (median 5.0% vs. 14.5%, P=0.017). PFS and OS was shortest for patients with persistent ctDNA at 4 weeks (univariate hazard ratio 4.79 (95%CI, 2.62-8.77) and 5.49 (95%CI, 2.76-10.91), respectively), independent of clinical prognostic factors. For patients exhibiting change from detected to undetected ctDNA by 4-weeks, there was no significant PFS difference versus patients with baseline undetected ctDNA. CtDNA change had a positive predictive value of 88% and negative predictive value of 92% for identifying non-durable responses.

CONCLUSIONS

Early changes in ctDNA% are strongly linked to duration of first-line ARPI treatment benefit and survival in mCRPC and may inform early therapy switches or treatment intensification.

Systemic exposure to cisplatin and paclitaxel after intraperitoneal chemotherapy in ovarian cancer

PURPOSE

To determine the systemic exposure to cisplatin and paclitaxel after adjuvant intraperitoneal administration in patients with advanced ovarian cancer who underwent primary debulking surgery. This could provide an explanation for the high incidence of systemic adverse events associated with this treatment regimen.

METHODS

This is a prospective pharmacokinetic study in patients with newly diagnosed advanced ovarian cancer who were treated with intraperitoneal administered cisplatin and paclitaxel. Plasma and peritoneal fluid samples were obtained during the first treatment cycle. The systemic exposure to cisplatin and paclitaxel was determined and compared to previously published exposure data after intravenous administration. An exploratory analysis was performed to investigate the relation between systemic exposure to cisplatin and the occurrence of adverse events.

RESULTS

Pharmacokinetics of ultrafiltered cisplatin were studied in eleven evaluable patients. The geometric mean [range] peak plasma concentration (C_max) and area under the plasma-concentration time curve (AUC_0-24 h) for cisplatin was 2.2 [1.8-2.7] mg/L and 10.1 [9.0-12.6] mg h/L, with a coefficient of variation (CV%) of 14 and 13.0%, respectively. The geometric mean [range] observed plasma concentration of paclitaxel was 0.06 [0.04-0.08] mg/L. No correlation was found between systemic exposure to ultrafiltered cisplatin and adverse events.

CONCLUSION

Systemic exposure to ultrafiltered cisplatin after intraperitoneal administration is high. In addition to a local effect, this provides a pharmacological explanation for high incidence of adverse events seen after intraperitoneal administration of high-dose cisplatin. The study was registered at ClinicalTrials.gov under registration number NCT02861872.

Feasibility of therapeutic drug monitoring of sorafenib in patients with liver or thyroid cancer

INTRODUCTION

Sorafenib is a tyrosine-kinase inhibitor approved for the treatment of renal cell carcinoma, hepatocellular carcinoma, thyroid carcinoma, and desmoid fibromatosis. As high inter-individual variability exists in exposure, there is a scientific rationale to pursue therapeutic drug monitoring (TDM). We investigated the feasibility of TDM in patients on sorafenib and tried to identify sub-groups in whom pharmacokinetically (PK) guided-dosing might be of added value.

METHODS

We included patients who started on sorafenib (between October 2017 and June 2020) at the recommended dose of 400 mg BID or with a step-up dosing schedule. Plasma trough levels (C_trough) were measured at pre-specified time-points. Increasing the dose was advised if C_trough was below the target of 3750 ng/mL and toxicity was manageable.

RESULTS

A total of 150 samples from 36 patients were collected. Thirty patients (83 %) had a C_trough below the prespecified target concentration at a certain time point during treatment. Toxicity from sorafenib hampered dosing according to target C_trough in almost half of the patients. In 11 patients, dosing was adjusted based on C_trough. In three patients, this resulted in an adequate C_trough without additional toxicity four weeks after the dose increase. In the remaining eight patients, dose adjustment based on C_trough did not result in a C_trough above the target or caused excessive toxicity.

CONCLUSIONS

TDM for sorafenib is not of added value in daily clinical practice. In most cases, toxicity restricts the possibility of dose escalations.

Exposure-response analyses of cabozantinib in patients with metastatic renal cell cancer

Aim

In the registration trial, cabozantinib exposure ≥ 750 ng/mL correlated to improved tumor size reduction, response rate and progression free survival (PFS) in patients with metastatic renal cell cancer (mRCC). Because patients in routine care often differ from patients in clinical trials, we explored the cabozantinib exposure–response relationship in patients with mRCC treated in routine care.

Methods

Cabozantinib trough concentrations (C_min) were collected and average exposure was calculated per individual. Exposure–response analyses were performed using the earlier identified target of C_min > 750 ng/mL and median C_min. In addition, the effect of dose reductions on response was explored. PFS was used as measure of response.

Results

In total, 59 patients were included:10% were classified as favourable, 61% as intermediate and 29% as poor IMDC risk group, respectively. Median number of prior treatment lines was 2 (0–5). Starting dose was 60 mg in 46%, 40 mg in 42% and 20 mg in 12% of patients. Dose reductions were needed in 58% of patients. Median C_min was 572 ng/mL (IQR: 496–701). Only 17% of patients had an average C_min ≥ 750 ng/mL. Median PFS was 52 weeks (95% CI: 40–64). No improved PFS was observed for patients with C_min ≥ 750 ng/mL or ≥ 572 ng/ml. A longer PFS was observed for patients with a dose reduction vs. those without (65 vs. 31 weeks, p = .001). After incorporating known covariates (IMDC risk group and prior treatment lines (< 2 vs. ≥ 2)) in the multivariable analysis, the need for dose reduction remained significantly associated with improved PFS (HR 0.32, 95% CI:0.14–0.70, p = .004).

Conclusion

In these explorative analyses, no clear relationship between increased cabozantinib exposure and improved PFS was observed. Average cabozantinib exposure was below the previously proposed target in 83% of patients. Future studies should focus on validating the cabozantinib exposure required for long term efficacy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09338-1.

RNA Biomarkers as a Response Measure for Survival in Patients with Metastatic Castration-Resistant Prostate Cancer

Treatment evaluation in metastatic castration-resistant prostate cancer is challenging. There is an urgent need for biomarkers to discriminate short-term survivors from long-term survivors, shortly after treatment initiation. Thereto, the added value of early RNA biomarkers on predicting progression-free survival (PFS) and overall survival (OS) were explored. The RNA biomarkers: KLK3 mRNA, miR-375, miR-3687, and NAALADL2-AS2 were measured in 93 patients with mCRPC, before and 1 month after start of first-line abiraterone acetate or enzalutamide treatment, in two prospective clinical trials. The added value of the biomarkers to standard clinical parameters in predicting PFS and OS was tested by Harell's C-index. To test whether the biomarkers were independent markers of PFS and OS, multivariate Cox regression was used. The best prediction model for PFS and OS was formed by adding miR-375 and KLK3 (at baseline and 1 month) to standard clinical parameters. Baseline miR-375 and detectable KLK3 after 1 month of therapy were independently related to shorter PFS, which was not observed for OS. In conclusion, the addition of KLK3 and miR-375 (at baseline and 1 month) to standard clinical parameters resulted in the best prediction model for survival assessment.

Lost in third space: altered tyrosine-kinase inhibitor pharmacokinetics in a patient with malignant ascites

BACKGROUND

Pazopanib and sunitinib are oral tyrosine kinase inhibitors (TKI) approved for the treatment of renal cell carcinoma. For both oncolytics, a clear target trough concentration level in plasma has been defined above which improved clinical efficacy can be expected. However, many factors can alter TKI exposure, including disease characteristics.

CASE

A 79-year old male with metastatic papillary renal cell carcinoma and malignant ascites was treated with pazopanib. Initially, treatment with pazopanib at adequate trough concentrations resulted in regression of ascites. After a 6-month puncture-free interval, paracenteses were again required and the plasma trough concentration of pazopanib had decreased to 5 mg/L without any dose adjustments. Despite a dose increase, pazopanib levels remained subtherapeutic and could not prevent new paracenteses. Pazopanib concentrations in the drained ascites fluid were comparable to plasma concentrations and remained high also after treatment discontinuation. This observation suggests that the ascites compartment may act as a third space in which pazopanib accumulates. During subsequent treatment with sunitinib, a similar distribution over ascites fluid was observed.

CONCLUSION

Presence of ascites or pleural effusion in patients treated with TKIs may lead to subtherapeutic plasma exposure, which may hamper treatment efficacy. Measuring TKIs plasma concentrations regularly during treatment is essential to identify patients with subtherapeutic exposure.

Exposure-toxicity relationship of cabozantinib in patients with renal cell cancer and salivary gland cancer

Cabozantinib is registered in fixed 60 mg dose. However, 46% to 62% of patients in the registration studies needed a dose reduction due to toxicity. Improved clinical efficacy has been observed in renal cell carcinoma patients (RCC) with a cabozantinib exposure greater than 750 μg/L. In our study we explored the cabozantinib exposure in patients with different tumour types. We included RCC patients from routine care and salivary gland carcinoma (SGC) patients from a phase II study with ≥1 measured C_min at steady‐state. The geometric mean (GM) C_min at the starting dose, at 40 mg and at best tolerated dose (BTD) were compared between both tumour types. Forty‐seven patients were included. All SGC patients (n = 22) started with 60 mg, while 52% of RCC patients started with 40 mg. GM C_min at the start dose was 1456 μg/L (95% CI: 1185‐1789) vs 682 μg/L (95% CI: 572‐812) (P < .001) for SGC and RCC patients, respectively. When dose‐normalised to 40 mg, SGC patients had a significantly higher cabozantinib exposure compared to RCC patients (C_min 971 μg/L [95% CI: 790‐1193] vs 669 μg/L [95% CI: 568‐788]) (P = .005). Dose reductions due to toxicity were needed in 91% and 60% of SGC and RCC patients, respectively. Median BTD was between 20 to 30 mg for SGC and 40 mg for RCC patients. GM C_min at BTD were comparable between the SGC and the RCC group, 694 μg/L (95% CI: 584‐824) vs 583 μg/L (95% CI: 496‐671) (P = .1). The observed cabozantinib exposure at BTD of approximately 600 μg/L is below the previously proposed target. Surprisingly, a comparable exposure at BTD was reached at different dosages of cabozantinib for SGC patients compared to RCC patients Further research is warranted to identify the optimal exposure and starting dose to balance efficacy and toxicity.

What's new?

Cabozantinib, a potent tyrosine kinase inhibitor that targets multiple signaling pathways, is approved for use against advanced renal cell carcinoma (RCC). Variations in cabozantinib clearance, however, warrant further investigation. Here, the authors evaluated cabozantinib exposure in RCC patients and in patients with salivary gland cancer (SGC). SGC patients were found to have significantly higher cabozantinib exposure compared to RCC patients following a 40 mg dose. However, the best‐tolerated cabozantinib exposure was equivalent (~600 μg/L) for both tumor types and was substantially below the previously proposed target. The findings offer insight on exposure, dose, and the balance between efficacy and toxicity for cabozantinib.

The effect of chemotherapy on the exposure-response relation of abiraterone in metastatic castration-resistant prostate cancer

Aims

To assess whether the exposure–response relation for abiraterone is different in pre‐chemotherapy patients compared to post‐chemotherapy patients with metastatic castration‐resistant prostate cancer (mCRPC).

Methods

Data were collected from three clinical studies in mCRPC patients treated with abiraterone acetate. Cox regression analysis was used to determine the relation between abiraterone exposure and survival (progression‐free survival [PFS] and overall survival [OS]). An interaction term was used to test whether chemotherapy pretreatment was an effect modifier. To investigate the effect of the previously defined exposure threshold of 8.4 ng/mL on survival, Kaplan–Meier analysis was used.

Results

In total, 98 mCRPC patients were included, of which 78 were pre‐chemotherapy and 20 were post‐chemotherapy patients. Chemotherapy pretreatment in mCRPC setting appears to be an effect modifier. In pre‐chemotherapy patients, no significant association between abiraterone exposure and survival was observed (HR 0.68 [95% CI 0.42–1.10], P = .12 and HR 0.85 [95% CI 0.46–1.60], P = .61, PFS and OS, respectively) and no longer survival was seen for patients with an abiraterone exposure above the predefined threshold. In contrast, a significant association was seen in post‐chemotherapy patients (HR 0.30 [95% CI 0.12–0.74], P = .01 and HR 0.38 [95% CI 0.18–0.82] P = .01, PFS and OS, respectively), with an increased survival when exposed above this threshold.

Conclusion

Chemotherapy pretreatment in mCRPC setting modifies the abiraterone exposure–response relation. No relation between abiraterone exposure and survival was seen for pre‐chemotherapy patients. Therefore, potentially lower doses can be used in this setting to prevent overtreatment and reduce financial toxicity.

Abstract 1363: Exposure-toxicity analysis of cabozantinib in patients with salivary gland cancer and renal cell cancer

Background

Cabozantinib is approved for treatment of renal cell cancer (RCC) in a starting dose of 60 mg. However, in the registration studies dose reductions were needed in 46-62% of patients due to toxicity. Improved clinical efficacy of cabozantinib was observed in RCC patients with an average exposure of &gt; 750 ug/L. Data about cabozantinib pharmacokinetics in patients routinely treated with this drug is scarce, while treatment is challenging due to toxicity. Therefore, we explored the cabozantinib exposure in patients with two different tumour types in our clinic.

Methods

Clinical data and cabozantinib trough concentrations (Cmin) were collected from all patients treated with cabozantinib with at least one measured Cmin at steady state in our clinic between Jan 2018 - Aug 2020. We included salivary gland cancer (SGC) patients treated in a phase II study and RCC patients from our outpatient clinic. Geometric mean (GM) Cmin at the start dose, at 40 mg and at best tolerated dose (BTD) were compared between the two tumour types.

Results

In total 47 patients were included. All patients with SGC (n=22) started with 60 mg, while 13 of 25 patients with RCC started with 40 mg. GM Cmin level at the start dose was 1350 µg/L (95% CI 1182-1781) vs. 689 µg/L (95% CI 576-823) (P&lt;.001) for patients with SGC and RCC, respectively. When dose-normalized to 40 mg, SGC patients had a significantly higher cabozantinib exposure compared to RCC patients (GM Cmin 968 µg/L (95% CI 788-1188) vs. 676 µg/L (95% CI 571-799)(P=.007). A higher cabozantinib GM Cmin level was observed in female compared to male patients. Dose reductions due to toxicity were needed in 91% and 60% of patients with SGC and RCC, respectively. Median BTD was 25 mg for SGC patients and 40 mg for RCC patients. GM Cmin at BTD were comparable between the SGC group and the RCC group, i.e. 692 µg/L (95% CI 582-822) vs. 576 µg/L (95% CI 493-673) (P=.1), respectively. At BTD, 64% of SGC patients and 80% of RCC patients had an exposure below the proposed target of &gt;750 ug/L.

Conclusion

Unexpectedly, cabozantinib levels were significantly higher in patients with SGC compared to those with RCC at the dose of 40 mg. However, cabozantinib levels at BTD were comparable between patients with SGC and RCC. At BTD, the majority of patients did not reach the target of &gt;750 µg/L. For most patients with RCC, the cabozantinib level at BTD corresponded to a dose of 40 mg. Therefore, 40 mg instead of 60 mg as a starting dose followed by dose-adjustment based on exposure and tolerability may be preferred in patients with RCC. Although cabozantinib is not registered for SGC, an even lower starting dose of 20 mg/day may be required in these patients based on cabozantinib levels at BTD. Future studies should focus on identifying an optimal and tolerable exposure-response target value for cabozantinib and elucidate factors that contribute to the differences in exposure, in order to individualise and improve treatment.

Citation Format: Stefanie D. Krens, Wim van Boxtel, Maike J. Uijen, Frank G. Jansman, Ingrid M. Desar, Sasja F. Mulder, Carla M. van Herpen, Nielka P. van Erp. Exposure-toxicity analysis of cabozantinib in patients with salivary gland cancer and renal cell cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1363.

Liquid biopsy reveals KLK3 mRNA as a prognostic marker for progression free survival in patients with metastatic castration-resistant prostate cancer undergoing first-line abiraterone acetate and prednisone treatment

Circulating RNAs extracted from liquid biopsies represent a promising source of cancer‐ and therapy‐related biomarkers. We screened whole blood from patients with metastatic castration‐resistant prostate cancer (mCRPC) following their first‐line treatment with abiraterone acetate and prednisone (AA‐P) to identify circulating RNAs that may correlate with progression‐free survival (PFS). In a prospective multicenter observational study, 53 patients with mCRPC were included after they started first‐line AA‐P treatment. Blood was drawn at baseline, 1, 3, and 6 months after treatment initiation. The levels of predefined circulating RNAs earlier identified as being upregulated in patients with mCRPC (e.g., microRNAs, long noncoding RNAs, and mRNAs), were analyzed. Uni‐ and multivariable Cox regression and Kaplan–Meier analyses were used to analyze the prognostic value of the various circulating RNAs for PFS along treatment. Detectable levels of kallikrein‐related peptidase 3 (KLK3) mRNA at baseline were demonstrated to be an independent prognostic marker for PFS (201 vs 501 days, P = 0.00054). Three months after AA‐P treatment initiation, KLK3 could not be detected in the blood of responding patients, but was still detectable in 56% of the patients with early progression. Our study confirmed that KLK3 mRNA detection in whole blood is an independent prognostic marker in mCRPC patients receiving AA‐P treatment. Furthermore, the levels of circulating KLK3 mRNA in patients receiving AA‐P treatment might reflect treatment response or early signs of progression.

High-dose administration of tyrosine kinase inhibitors to improve clinical benefit: A systematic review

BACKGROUND

Innovative strategies to fully exploit the antitumor activity of multitargeted tyrosine kinase inhibitors (TKIs) are urgently needed. Higher concentrations of TKIs at their target site, i.e. intratumorally, may lead to broader kinase inhibition, which might be essential for the optimal suppression of tumor growth and induction of apoptosis. To reach these higher intratumoral concentrations, without encountering dose limiting toxicity, alternative TKI dosing strategies employing higher daily and high intermittent doses have been studied. In this systematic review, we evaluated the current clinical evidence to support (intermittent) high TKI dosing regimens.

METHODS

A systematic review was conducted in the following databases: PubMed®, EMBASE® and Cochrane Library©, to evaluate efficacy of alternatively scheduled high-dosed regimen (a higher dose in a regular daily schedule than registered or a higher dose in an alternative intermittent schedule) of TKIs in (haemato-)oncology. Data were extracted independently by two authors according to predefined criteria. Extracted data were tabulated to summarize key findings.

RESULTS

Out of twenty studies that met the inclusion criteria, thirteen investigated higher daily dose schedules of either afatinib, axitinib, erlotinib, gefitinib, imatinib, sorafenib, and sunitinib. Five of these studies included pharmacokinetic analyses, reporting marginal higher maximum drug concentrations (C_max) in plasma (1.3-4-fold higher) compared to the standard dose schedules. Seven clinical trials investigated intermittent high-dose schedules requiring treatment breaks, with the following TKIs: afatinib, erlotinib, gefitinib, lapatinib, sorafenib, and sunitinib. Six of these included pharmacokinetic results, all reporting higher (2-21-fold) C_max in plasma compared to the standard daily dose schedule, with manageable toxicity. No data on tumor concentrations were presented. Data on the efficacy outcomes were limited due to small sample size, study designs, phase 1 population and heterogeneous tumor types.

CONCLUSIONS

Early phase clinical studies show that high-dose intermittent TKI-treatment schedules can lead to an increased C_max compared to standard (low-dose) daily administration with manageable toxicity. These higher concentrations are assumed to reflect higher intratumoral concentrations. Further investigation of the potential improvement in clinical benefit of a high-dose intermittent strategy with multitargeting TKIs is warranted.

Pressurized Intraperitoneal Aerosol Chemotherapy: The Road from Promise to Proof

Pressurized intraperitoneal aerosol chemotherapy (PIPAC) is an innovative drug delivery technique invented to be used for the treatment of peritoneal metastasis. Its application gained popularity over the past years. Several prospective clinical trials are being conducted to determine efficacy and safety. At this moment, there remain many challenges to overcome before PIPAC can be widely adopted in clinical practice.See related article by Kim et al., p. 1875.

The impact of a 1-hour time interval between pazopanib and subsequent intake of gastric acid suppressants on pazopanib exposure

Co‐treatment with gastric acid suppressants (GAS) in patients taking anticancer drugs that exhibit pH‐dependant absorption may lead to decreased drug exposure and may hamper drug efficacy. In our study, we investigated whether a 1‐hour time interval between subsequent intake of pazopanib and GAS could mitigate this negative effect on drug exposure. We performed an observational study in which we collected the first steady‐state pazopanib trough concentration (C_min) levels from patients treated with pazopanib 800 mg once daily (OD) taken fasted or pazopanib 600 mg OD taken with food. All patients were advised to take GAS 1 hour after pazopanib. Patients were grouped based on the use of GAS and the geometric (GM) C_min levels were compared between groups for each dose regimen. Additionally, the percentage of patients with exposure below the target threshold of 20.5 mg/L and the effect of the type of PPI was explored. The GM C_min levels were lower in GAS users vs non‐GAS users for both the 800 and 600 mg cohorts (23.7 mg/L [95% confidence interval [CI]: 21.1‐26.7] vs 28.2 mg/L [95% CI: 25.9‐30.5], P = .015 and 26.0 mg/L [95% CI: 22.4‐30.3] vs 33.5 mg/L [95% CI: 30.3‐37.1], P = .006). Subtherapeutic exposure was more prevalent in GAS users vs non‐GAS users (33.3% vs 19.5% and 29.6% vs 14%). Sub‐analysis showed lower GM pazopanib C_min in patients who received omeprazole, while minimal difference was observed in those receiving pantoprazole compared to non‐users. Our research showed that a 1‐hour time interval between intake of pazopanib and GAS did not mitigate the negative effect of GAS on pazopanib exposure and may hamper pazopanib efficacy.

A Systematic Review and Meta-Analysis on the Predictive Value of Cell-Free DNA–Based Androgen Receptor Copy Number Gain in Patients With Castration-Resistant Prostate Cancer

PURPOSE

It has been suggested that androgen receptor copy number gain ( AR gain) detected in cell-free DNA (cfDNA) can predict treatment response to androgen receptor signaling inhibitors (ARSIs) in patients with castration-resistant prostate cancer (CRPC). But it is unclear whether cfDNA-based AR gain is a true resistance mechanism to ARSIs or mainly a reflection of the tumor burden. In this systematic review, we aim to summarize current literature and comment on the potential of cfDNA-based AR gain as a predictive biomarker to guide therapy choices.

METHODS

A literature search was conducted in PubMed/Medline, Cochrane, Embase, and Web of Science databases. Sixteen articles published before November 2019 were selected for the meta-analysis, representing more than 1,000 patients. By using a random effects model, the progression-free survival (PFS) and overall survival (OS) were compared between patients with and without cfDNA-based AR gain who had been treated with ARSIs or with taxane chemotherapy.

RESULTS

Upon treatment with ARSIs, the PFS (hazard ratio [HR], 2.33; 95% CI, 2.00 to 2.72; P < .0001) and the OS (HR, 3.83; 95% CI, 3.11 to 4.70; P < .0001) were worse for patients with cfDNA-based AR gain, independent of the line and type of ARSIs. The OS and PFS in patients treated with first-line docetaxel or second-line or third-line cabazitaxel seemed to be unaffected by AR gain, despite a higher disease burden in patients with AR gain. AR gain was associated with reduced response with later lines of docetaxel.

CONCLUSION

In patients with CRPC, cfDNA-based AR gain is associated with a worse response to ARSIs. The effect on patients who are receiving taxane chemotherapy seems to be dependent on the type and line, although data are limited. Future prospective studies are essential to assess the true potential of cfDNA-based AR gain as a minimally invasive biomarker to guide therapy choice.

Abstract 1413: Exploring the prognostic value of microRNAs and drug exposure in patients with metastatic castration resistant prostate cancer treated with abiraterone: a prospective observational study

Background Abiraterone acetate is registered for treatment of metastatic prostate cancer, including those with castration-resistant disease (mCRPC). Although it improves overall survival and progression free survival (PFS), treatment response differs between patients. Biomarkers to predict treatment response are lacking. Liquid biopsies containing microRNAs (miRNAs) are a promising source of prognostic biomarkers in mCRPC patients. Furthermore, the exposure to abiraterone in plasma is highly variable and subtherapeutic exposure might contribute to the variability in response to therapy. We explored the prognostic value of microRNAs and drug exposure in mCRPC patients treated with abiraterone.

Methods In a prospective multi-center observational study, 53 patients with mCRPC were included who started pre-chemotherapy abiraterone treatment. Blood was drawn at baseline, 1, 3 and 6 months after start of treatment. The following predefined miRNAs were selected; miR-21, miR-141, miR-200a, miR-200c, miR-375, miR-3687 and abiraterone concentrations were measured. MiRNA-levels in 30 healthy individuals served as controls. Relative miRNA-levels were calculated by the ΔΔCt method. If the geometric mean of a miRNA was more than 2-fold higher in patients versus healthy controls, they were included for survival analysis. Ctrough levels after 1, 3 and 6 months of therapy were measured. The average Ctrough level per patient was used for further analysis. The prognostic value of miRNAs and drug exposure for PFS (radiographic, biochemical or clinical progression) was analyzed with Kaplan-Meier (KM) analysis and tested with a log-rank test. Cut-off values for miRNAs in KM analysis were calculated using maximally selected rank statistics and for the relation with abiraterone Ctrough the earlier defined threshold of 8.4ng/ml was used.

Results Of the miRNAs analyzed, miR-375 was more than 2-fold higher in mCRPC patients versus healthy controls. Patients with more than 2.16 fold higher miR-375 compared to healthy controls showed a trend towards shorter PFS, median 352 vs. 456 days (p=0.076). No PFS benefit was shown for patients with a mean abiraterone Ctrough concentration ≥8.4ng/ml compared to patients below this threshold, median 411 vs. 409 days (p=0.81).

Conclusion High levels of miR-375 might be a prognostic biomarker for PFS in patients with mCRPC treated with abiraterone. The prognostic value of this miRNA should be further explored in a larger cohort of patients. Additionally, the functionality of miR-375 should be further elucidated. The beneficial effect of higher abiraterone exposure levels could not be confirmed in this study for this patient population.

Citation Format: Emmy Boerrigter, Guillemette E. Benoist, Inge M. van Oort, Gerald W. Verhaegh, Onno van Hooij, Levi Groen, Frank Smit, Irma M. Oving, Pieter de Mol, Tineke J. Smilde, Diederik M. Somford, Niven Mehra, Jack A. Schalken, Nielka P. van Erp. Exploring the prognostic value of microRNAs and drug exposure in patients with metastatic castration resistant prostate cancer treated with abiraterone: a prospective observational study [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1413.

Wide variation in tissue, systemic, and drain fluid exposure after oxaliplatin-based HIPEC: results of the GUTOX study

Purpose

In this exploratory study, the effect of postprocedural flushing with crystalloids after oxaliplatin-based hyperthermic intraperitoneal chemotherapy (HIPEC) on platinum concentrations in peritoneal tissue, blood, and drain fluid was studied. Interpatient variability in oxaliplatin pharmacokinetics and the relation between platinum concentration in peritoneal fluid and platinum exposure in tissue and blood was explored.

Methods

Ten patients with peritoneal carcinomatosis of colorectal origin were treated with HIPEC including postprocedural flushing, followed by ten patients without flushing afterwards. Tissue, peritoneal fluid, blood, and drain fluid samples were collected for measurement of total and ultrafiltered platinum concentrations.

Results

Peritoneal tissue concentration and systemic ultrafiltered platinum exposure showed large inter individual variability, ranging from 65 to 1640 µg/g dry weight and 10.5 to 28.0 µg*h/ml, respectively. No effect of flushing was found on geometric mean platinum concentration in peritoneal tissue (348 vs. 356 µg/g dry weight), blood (14.8 vs. 18.1 µg*h/ml), or drain fluid (day 1: 7.6 vs. 7.7 µg/ml; day 2: 1.7 vs. 1.9 µg/ml). The platinum concentration in peritoneal fluid at the start of HIPEC differed twofold between patients and was positively correlated with systemic exposure (p = .04) and peak plasma concentration (p = .04).

Conclusion

In this exploratory study, no effect was found for postprocedural flushing on platinum concentrations in peritoneal tissue, blood, or drain fluid. BSA-based HIPEC procedure leads to large interpatient variability in platinum exposure in all compartments.

The study was registered at ClinicalTrials.gov on 7 December 2017 under registration number NCT03364907.

Dose recommendations for anticancer drugs in patients with renal or hepatic impairment

Renal or hepatic impairment is a common comorbidity for patients with cancer either because of the disease itself, toxicity of previous anticancer treatments, or because of other factors affecting organ function, such as increased age. Because renal and hepatic function are among the main determinants of drug exposure, the pharmacokinetic profile might be altered for patients with cancer who have renal or hepatic impairment, necessitating dose adjustments. Most anticancer drugs are dosed near their maximum tolerated dose and are characterised by a narrow therapeutic index. Consequently, selecting an adequate dose for patients who have either hepatic or renal impairment, or both, is challenging and definitive recommendations on dose adjustments are scarce. In this Review, we discuss the effect of renal and hepatic impairment on the pharmacokinetics of anticancer drugs. To guide clinicians in selecting appropriate dose adjustments, information from available drug labels and from the published literature were combined to provide a practical set of recommendations for dose adjustments of 160 anticancer drugs for patients with hepatic and renal impairment.

The relationship between sunitinib exposure and both efficacy and toxicity in real-world patients with renal cell carcinoma and gastrointestinal stromal tumour

Aim

Sunitinib is an oral tyrosine kinase inhibitor approved for the treatment of renal cell carcinoma (RCC) and gastrointestinal stromal tumor (GIST). Because of the large interpatient pharmacokinetic variability and established exposure‐response and exposure‐toxicity relationships in clinical trial patients, therapeutic drug monitoring (TDM) seems promising for optimizing sunitinib exposure. We aimed to investigate the relationship between sunitinib exposure and treatment outcome in a real‐world patient cohort.

Methods

We performed a retrospective observational cohort study in 53 patients with metastatic RCC and 18 patients with metastatic GIST treated with sunitinib and receiving TDM‐guided dosing. Time on treatment – as a surrogate for progression‐free survival – in patients who achieved adequate sunitinib exposure was compared with patients who did not. Additionaly, the median sunitinib exposure was compared in patients with or without sunitinib‐induced toxicity leading to dose reduction.

Results

The median time on treatment in patients with RCC who achieved adequate sunitinib exposure (n = 39) was 32 weeks, compared to 15 weeks in patients who did not achieve adequate sunitinib exposure (n = 12) (P = 0.244). In 29 patients (41%) with toxicity leading to dose reduction, sunitinib sum plasma trough concentration (C_trough) until dose reduction was significantly higher compared to patients without toxicity leading to dose reduction (median 60 ng/mL vs 44 ng/mL; P < 0.001) and reduced to comparable levels after dose reduction (44 ng/mL; P = 0.488).

Conclusion

In our real‐world patient cohort, patients with sunitinib‐induced toxicity requiring dose reduction had significantly higher sunitinib exposure compared to patients without toxicity. The threshold for toxicity, however, was lower compared to that previously described in clinical trials.

Prospective Study of Drug-induced Interstitial Lung Disease in Advanced Breast Cancer Patients Receiving Everolimus Plus Exemestane

BACKGROUND

Everolimus-related interstitial lung disease (ILD) (also: pneumonitis) poses a difficulty for physicians, as it is hard to discriminate ILD from other causes of respiratory symptoms and to decide on safe treatment continuation.

OBJECTIVE

We investigated the capability of pulmonary function tests (PFT), plasma biomarkers, everolimus pharmacokinetics, and FDG-PET to discriminate between everolimus-related ILD and other causes of respiratory problems and to predict the severity of ILD.

PATIENTS AND METHODS

Women starting treatment with everolimus plus exemestane for advanced breast cancer were included. At baseline and during the first 3 months, respiratory symptoms, PFT with diffusion capacity of the lungs for carbon monoxide corrected for hemoglobin (DLCOc) and forced vital capacity, serum plasma biomarkers (including SP-D and YKL-40), everolimus trough concentration, and ¹⁸F-FDG-PET were prospectively recorded.

RESULTS

Twenty-seven (out of 29 included) patients were evaluable for analysis. Fifteen patients (56%) developed everolimus-related respiratory signs or symptoms and four patients (15%) needed everolimus discontinuation and received corticosteroids. Change in DLCOc differentiated ILD from alternative diagnoses with 0.91 sensitivity and 0.78 specificity. Decrease in DLCOc (non-significant) was greatest in patients who needed everolimus discontinuation. Serum SP-D and YKL-40 could differentiate ILD from alternative diagnoses with 0.83 and 0.83 sensitivity, and 0.85 and 0.62 specificity, respectively. ¹⁸F-FDG-PET abnormalities did not precede clinical symptoms. No relationship between ILD and everolimus trough concentration was found.

CONCLUSIONS

This study shows that everolimus-related ILD occurs frequently. Prospective monitoring of DLCOc in combination with measurement of serum SP-D and YKL-40 appear useful to discriminate ILD from other causes of respiratory symptoms. Clinicaltrials.gov identifier: NCT01978171.

Imatinib, sunitinib and pazopanib: From flat-fixed dosing towards a pharmacokinetically guided personalized dose

Tyrosine kinase inhibitors (TKIs) are anti‐cancer drugs that target tyrosine kinases, enzymes that are involved in multiple cellular processes. Currently, multiple oral TKIs have been introduced in the treatment of solid tumours, all administered in a fixed dose, although large interpatient pharmacokinetic (PK) variability is described. For imatinib, sunitinib and pazopanib exposure‐treatment outcome (efficacy and toxicity) relationships have been established and therapeutic windows have been defined, therefore dose optimization based on the measured blood concentration, called therapeutic drug monitoring (TDM), can be valuable in increasing efficacy and reducing the toxicity of these drugs.

In this review, an overview of the current knowledge on TDM guided individualized dosing of imatinib, sunitinib and pazopanib for the treatment of solid tumours is presented. We summarize preclinical and clinical data that have defined thresholds for efficacy and toxicity. Furthermore, PK models and factors that influence the PK of these drugs which partly explain the interpatient PK variability are summarized. Finally, pharmacological interventions that have been performed to optimize plasma concentrations are described. Based on current literature, we advise which methods should be used to optimize exposure to imatinib, sunitinib and pazopanib.

Quantification of cobimetinib, cabozantinib, dabrafenib, niraparib, olaparib, vemurafenib, regorafenib and its metabolite regorafenib M2 in human plasma by UPLC-MS/MS

A sensitive and selective ultra‐high performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) method for the simultaneous determination of seven oral oncolytics (two PARP inhibitors, i.e. olaparib and niraparib, and five tyrosine kinase inhibitors, i.e. cobimetinib, cabozantinib, dabrafenib, vemurafenib and regorafenib, plus its active metabolite regorafenib M2) in EDTA plasma was developed and validated. Stable isotope‐labelled internal standards were used for each analyte. A simple protein precipitation method was performed with acetonitrile. The LC–MS/MS system consisted of an Acquity H‐Class UPLC system, coupled to a Xevo TQ‐S micro tandem mass spectrometer. The compounds were separated on a Waters CORTECS UPLC C18 column (2.1 × 50 mm, 1.6 μm particle size) and eluted with a gradient elution system. The ions were detected in the multiple reaction monitoring mode. The method was validated for cobimetinib, cabozantinib, dabrafenib, niraparib, olaparib, vemurafenib, regorafenib and regorafenib M2 over the ranges 6–1000, 100–5000, 10–4000, 200–2000, 200–20,000, 5000–100,000, 500–10,000 and 500–10,000 μg/L, respectively. Within‐day accuracy values for all analytes ranged from 86.8 to 115.0% with a precision of <10.4%. Between‐day accuracy values ranged between 89.7 and 111.9% with a between‐day precision of <7.4%. The developed method was successfully used for guiding therapy with therapeutic drug monitoring in cancer patients and clinical research programs in our laboratory.

Abstract C079: Effect of food on the pharmacokinetics of high dose intermittent sunitinib in patients with advanced solid tumors

Background: Optimization of the clinical use of multi-targeting tyrosine kinase inhibitors (TKIs), as sunitinib, is needed to fully exploit their potential antitumor activity. Sunitinib was developed to inhibit angiogenesis-related kinases, but at conventional daily dosing it also directly inhibits tumor cell growth. The inhibitory activity of sunitinib is dependent on its discriminative affinity for specific kinases, its intracellular concentrations reached at the tumor level and the presence and activity of kinases in tumor cells. Administration of sunitinib in a higher dose, similar to convential chemotherapy, might further utilize this direct antitumor effect and the strong broad kinase inhibitory potency of sunitinib. In a recent phase I trial of high dose intermittent sunitinib the maximum tolerated dose of 700 mg once every two weeks (Q2W) resulted in high peak plasma concentrations (Cmax) of &gt;500 µg/l, without drug accumulation. 63% of 69 heavily pretreated patients with advanced cancer had clinical benefit, with similar toxicity compared to standard daily dosing. Pharmacokinetic (PK) evaluation showed significant interpatient variability of this alternative regimen. In the current study, we evaluated the effect of food on the interpatient variation in bioavailability and studied whether food would further increase Cmax. Methods: 700 mg sunitinib Q2W was administered to patients with refractory solid tumors. Patients were randomized to either start sunitinib after a 10-hour fasted regimen or within 30 minutes after a high fat meal followed by the alternative at the second cycle. PK and safety assessments were obtained. Treatment continued until progression or unacceptable toxicity. Drug plasma concentrations were measured by LC-MS/MS. Geometric mean ratios (GMR) and 90% confidence intervals (CI) of the sum concentration of sunitinib and SU12662 were estimated. Results:Twelve patients were included. Both intake regimens were not bioequivalent. The GMR (fed/fasted) of the AUC0-µ and Cmax were 1.33 (90% CI 1.03-1.70) and 1.30 (90% CI 1.02-1.65), respectively. Compared with the fasted state, a high-fat meal delayed time to maximum plasma concentration by 1.6 hours. The observed non bioequivalence and increase in drug exposure appeared to be mainly caused by 2 patients who suffered from early vomiting (~3hrs) after drug ingestion in the fasted state. After excluding them from the analysis, the GMR of the AUC0-µ and Cmax change to 1.09 (90% CI 0.98-1.22) and 1.09 (90% CI 0.96-1.23), respectively, indicating that both regimens were bioequivalent. The interpatient variability for AUC0-µ was reduced by the intake of food; 32.5% (fasted) to 29% (fed), while for Cmax the interpatient variability was similar 34.4% and 33.3%. Adverse events were similar to our prior phase I study with mainly grade I-II toxicities including fatigue (58%), nausea (50%) and anorexia (42%). Conclusions: Our study demonstrates that high dose sunitinib can be taken with or without food. For the patients without GI toxicity early after intake, the exposure to sunitinib was bioequivalent. Interpatient variability appeared to be modestly reduced by taken sunitinib with food. The results support the recommendation for administration of high dose sunitinib in a fed state to achieve more consistent therapeutic exposure and increased tolerance. Results from ongoing phase II trials with high dose intermittent sunitinib for patients with colorectal cancer and glioblastoma are eagerly awaited.

Citation Format: Sophie L. Gerritse, Mariette Labots, Maria Rovithi, Angela Colbers, Olaf J.L. Loosveld, Mikkjal Skardhamar, Nielka P. van Erp, Henk M.W. Verheul. Effect of food on the pharmacokinetics of high dose intermittent sunitinib in patients with advanced solid tumors [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C079. doi:10.1158/1535-7163.TARG-19-C079

A prospective phase I multicentre randomized cross-over pharmacokinetic study to determine the effect of food on abiraterone pharmacokinetics

Purpose

Abiraterone acetate is used at a fixed oral dose of 1000 mg once daily (OD) taken fasted. By administering abiraterone acetate with food, a reduced dose can potentially be given while maintaining equivalent abiraterone exposure. Moreover, administering abiraterone acetate with a breakfast is considered more patient friendly. The aim of this study was to establish the bio-equivalent lower dose of abiraterone when taken with a continental breakfast (CB) compared to the standard intake of 1000 mg OD fasted.

Methods

In this phase I, randomized cross-over, multi-center study, abiraterone pharmacokinetics (PK) were evaluated in patients with metastatic castration-resistant prostate cancer who were treated for 14 days with 1000 mg abiraterone acetate taken fasted, followed by 14 days of treatment with 500 mg taken with a CB.

Results

14 patients were enrolled into the study, of whom 12 were eligible for PK analysis. The geometric mean ratio (GMR) (fed/fasted) was 0.88 (90% CI 0.73–1.07) for area-under-the-curve (AUC_0–24h), 1.03 (90% CI 0.79–1.34) for C_max and 0.81 (90% CI 0.60–1.10) for C_trough, respectively. High inter-patient variability (> 50%) was found for all PK parameters under both intake conditions. Patients seemed to be slightly more satisfied about the intake of 500 mg abiraterone acetate when taken with a CB compared to 1000 mg fasted.

Conclusion

In conclusion, a bioequivalent lower dose of abiraterone taken with food could not be established in our study. Although based on the absence of a exposure–toxicity relationship, the strict bioequivalence margins as defined by the FDA guidelines could be applied more flexible for abiraterone. Information on the effect of food on abiraterone pharmacokinetics as presented in our study can be used for patients with difficulties taken their medication fasted.

Electronic supplementary material

The online version of this article (10.1007/s00280-019-03952-w) contains supplementary material, which is available to authorized users.

The effect of gastrectomy on regorafenib exposure and progression-free survival in patients with advanced gastrointestinal stromal tumours

Aims

We investigated whether major gastrectomy influences the plasma exposure of regorafenib and treatment outcome.

Methods

Efficacy and pharmacokinetic data from 133 gastrointestinal stromal tumour patients included in a phase III trial were analysed. Patients were subdivided into 2 groups according to the extent of the gastrectomy (no/nonsignificant gastrectomy and major gastrectomy). Progression‐free survival (PFS) on regorafenib was measured and regorafenib and its pharmacological active metabolites plasma exposure were measured.

Results

A total of 133 patient were included, of whom 27 underwent major gastrectomy. In patients with no/nonsignificant gastrectomy the median PFS was 145 (interquartile range 43–281) days. The PFS in patients with a major gastrectomy was 172 (interquartile range 57–280) days. Regorafenib pharmacokinetic samples were collected in 80 patients of which 19 patients with a major gastrectomy and 61 patients with no/nonsignificant gastric surgery. The average ± standard deviation total concentration of regorafenib including the metabolites M‐2 and M‐5 was 6.9 ± 1.53 μmol/L and 6.7 ± 1.56 μmol/L in patient with major gastrectomy and no/nonsignificant gastrectomy respectively.

Conclusion

Our study shows that major gastrectomy did not influence plasma exposure of regorafenib and metabolites. In addition, no difference in PFS between the subgroups was seen.

Simple and Rapid Quantification of the Multi-Enzyme Targeting Antifolate Pemetrexed in Human Plasma

BACKGROUND

Pemetrexed is an antifolate cytostatic drug that targets multiple enzymes involved in folate biosynthesis and is indicated for treatment of non-small-cell lung cancer and malignant pleural mesothelioma. As evidence for an exposure-response/toxicity relationship is accumulating, dose individualization using therapeutic drug monitoring may be a feasible strategy to optimize treatment. The purpose of this study was to develop a simple, sensitive, high-performance liquid chromatography method with UV detection for quantification of pemetrexed levels in human plasma.

METHOD

The method involves a simple protein precipitation, followed by ultra-performance liquid chromatography with ultraviolet detection at a wavelength of 254 nm. Pemetrexed was separated using a mobile phase with a linear gradient and a run time of only 7 minutes.

RESULTS

The assay has been validated over the concentration range 0.25-500 mg/L of pemetrexed. Accuracy for this assay ranged from -4.50% to 1.78%, and the within- and between-run coefficients of variation were <3.57%. Pemetrexed in plasma was proven to be stable for 8 months at -40°C.

CONCLUSIONS

The bioanalytical method we developed proved to be simple, accurate, precise, and fast. This analytical method is successfully in use for therapeutic drug monitoring and will be used for pharmacokinetic studies.

Optimizing the dose in patients treated with imatinib as first line treatment for gastrointestinal stromal tumours: A cost-effectiveness study

Aims

Patients with metastatic gastrointestinal stromal tumours (GIST) are treated in first line with the oral tyrosine kinase inhibitor, imatinib, until progressive disease. With this fixed dosing regimen, only approximately 40% of patients reach adequate plasma levels within the therapeutic index. Therapeutic drug monitoring (TDM) is a solution to reach plasma levels within the therapeutic index. However, introducing TDM will also increase costs, due to prolonged imatinib use and laboratory costs. The aim of this study was to evaluate the cost‐effectiveness of TDM in patients with metastatic/unresectable GIST treated with imatinib as a first line treatment, compared with fixed dosing.

Methods

A survival model was created to simulate progression, mortality and treatment costs over a 5‐year time horizon, comparing fixed dosing vs TDM‐guided dosing. The outcomes measured were treatments costs, life‐years and quality‐adjusted life‐years.

Results

Total costs over the 5‐year time horizon were estimated to be €106 994.85 and €150 477.08 for fixed dosing vs TDM‐guided dosing, respectively. A quality‐adjusted life year gain of 0.74 (95% confidence interval 0.66–0.90) was estimated with TDM‐guided dosing compared to fixed dosing. An average incremental cost‐effectiveness ratio of €58 785.70 per quality‐adjusted life year gained was found, mainly caused by longer use and higher dosages of imatinib.

Conclusion

Based on the currently available data, this analysis suggests that TDM‐guided dosing may be a cost‐effective intervention for patients with metastatic/unresectable GIST treated with imatinib which will be improved when imatinib losses its patency.

The Effect of Using Pazopanib With Food vs. Fasted on Pharmacokinetics, Patient Safety, and Preference (DIET Study)

Pazopanib is taken fasted in a fixed oral daily dose of 800 mg. We hypothesized that ingesting pazopanib with food may improve patients' comfort and reduce gastrointestinal (GI) adverse events. Therefore, we investigated the bioequivalent dose of pazopanib when taken with food compared with 800 mg pazopanib taken fasted. In addition, we investigated the differences in GI toxicity, patient satisfaction, and patient's preference for either intake. The intake of 600 mg pazopanib with food resulted in a bioequivalent exposure and was preferred over a standard pazopanib dose without food. No differences were seen in GI toxicities under both intake regimens. Patients seem to be more positive about their feelings about side effects and satisfaction with their therapy when pazopanib was taken with food. Forty-one of the patients (68%) preferred the intake with a continental breakfast.

Development and Validation of a Bioanalytical Method to Quantitate Enzalutamide and its Active Metabolite N-Desmethylenzalutamide in Human Plasma: Application to Clinical Management of Patients With Metastatic Castration-Resistant Prostate Cancer

BACKGROUND

Enzalutamide is a potent androgen-signaling receptor inhibitor and is licensed for the treatment of metastatic castration-resistant prostate cancer. N-desmethylenzalutamide is the active metabolite of enzalutamide. A method to quantitate enzalutamide and its active metabolite was developed and validated according to the European Medicine Agency guidelines.

METHODS

Enzalutamide and N-desmethylenzalutamide were extracted by protein precipitation, separated on a C18 column with gradient elution and analyzed with tandem quadrupole mass spectrometry in positive ion mode. A stable deuterated isotope (D6-enzalutamide) was used as an internal standard. The method was tested and stability was studied in real-life patients with metastatic castration-resistant prostate cancer patients treated with enzalutamide.

RESULTS

The calibration curve covered the range of 500-50,000 ng/mL. Within- and between-day precisions were <8% and accuracies were within 108% for both enzalutamide and N-desmethylenzalutamide. Precisions for lower limit of quantification level were <10% and accuracies within 116% for enzalutamide and N-desmethylenzalutamide. Enzalutamide and N-desmethylenzalutamide stability was proven for 24 hours for whole blood at ambient temperature and 23 days for plasma at both ambient temperature and 2-8°C. Long-term patient plasma stability was shown for 14 months at -40°C.

CONCLUSIONS

This bioanalytical method was successfully validated and applied to determine plasma concentrations of enzalutamide and N-desmethylenzalutamide in clinical studies and in routine patient care.

Hyperthermic intraperitoneal chemotherapy with oxaliplatin for peritoneal carcinomatosis: a clinical pharmacological perspective on a surgical procedure

Cytoreductive surgery combined with hyperthermic intraperitoneal chemotherapy (HIPEC) has become the standard of care in the treatment of patients with peritoneal carcinomatosis of colorectal origin. The use of oxaliplatin for HIPEC has gained popularity. Although the HIPEC procedure is adopted throughout the world, major differences exist between treatment protocols regarding the carrier solution, perfusate volume, use of an open or closed technique, duration of the perfusion and application of additional flushing. These differences can influence the pharmacokinetics and pharmacodynamics of oxaliplatin and might thereby have an impact on the efficacy and/or safety of the treatment. Clinicians should be aware of the clinical importance of oxaliplatin pharmacology when performing HIPEC surgery. This review adds new insights into the complex field of the pharmacology of HIPEC and highlights an important worldwide problem: the lack of standardization of the HIPEC procedure.